The present invention relates to a method for manufacturing a layer of an oxide-ceramic superconductor material with a high superconducting transition temperature and high current capacity, on the basis of a system containing metallic constituents and oxygen, whereby a target material of the system is vaporized and deposited on a predetermined substrate by means of a pulsed laser with a wavelength in the ultraviolet spectral range, and whereby, by applying a heat treatment and an oxygen treatment, the desired superconducting metal-oxide phase is formed with an at least partially ordered crystal structure. A corresponding method proceeds, for example, from the publication "Applied Physics Letters", Vol. 51, No. 11, Sep. 14, 1987, pages 861 to 863.
Superconductive metal-oxide compounds are generally known with high superconducting transition temperatures T.sub.c of especially over 90 K. These metal-oxide compounds can be based, for example, on a system of the Me1-Me2-Cu-O type, whereby the constituent Me1 contains at least a rare earth metal, such as for example Y, and Me2 contains at least an alkaline-earth metal, such as for example Ba. Films or thin layers made of these metal-oxide compounds are often manufactured using special vaporization or sputtering processes. Hereby, a polycrystalline or amorphous initial product with the constituents of the selected system is generally first deposited on a suitable substrate, whereby the oxygen content and consequently, the desired phase are usually not yet exactly established. This initial product is then converted, by applying a heat and oxygen treatment, into the material with the desired superconducting phase.
The superconductive metal-oxide phases, to be obtained in this manner, can have perovskite-like crystal structures and, in the case of YBa.sub.2 Cu.sub.3 O.sub.7-x, whereby O&lt;x&lt;0.5, have an orthorhomic structure (compare, for example, "Europhysics Letters", Vol. 3, No. 12, Jun. 15, 1987, pages 1301 to 1307). Their superconducting transition temperature T.sub.c lies, thereby, at approximately 90 K. Since the materials showing these superconducting phases are to be classed with oxide-ceramics, the corresponding high-T superconductors are also often designated as oxide-ceramic superconductors.
Manufacturing single-crystal films of the YBa.sub.2 Cu.sub.3 O.sub.7-x system on a single-crystal SrTiO.sub.3 substrate by way of epitaxy is a known procedure from the publication mentioned above, "Applied Physics Letters". For this purpose, a target material of the mentioned system is first vaporized by a laser and separated on to the substrate with the ordered crystal structure The laser used in this instance is a KrF-excimer laser with a wavelength of radiation in the ultraviolet (uv) spectral range. It can be focused to produce a power density at the target material of approximately 2 J/cm.sup.2, at a pulse frequency of 3 to 6 Hz. The subtrate is thereby heated to 450.degree. C. (compare also "Appl.Phys.Lett.", Vol. 51, No. 8, Aug. 24, 1987, pages 619 to 621). However, the layer obtained in this manner is still defectively structured, as far as the desired superconducting high-T.sub.c phase is concerned. By following with a heat treatment at a high temperature of approximately 900.degree. C. in an oxygen atmosphere and, with a subsequent slow cooling, one then obtains epitactically grown single-crystal or at least heavily textured film layers with the desired superconducting high-T.sub.c phase.
Such film layers distinguish themselves by high critical current densities, which at 77 K can amount to over 10.sup.5 A/cm.sup.2. The mentioned epitaxy is thereby considered as a prerequisite for attaining such high, critical current densities. However, using the known method to manufacture the appropriate layers entails considerable expenditure. In addition, the epitaxy, which takes place in the high temperature process is difficult to control. In particular, an interdiffusion between the film material and the substrate cannot be avoided in many cases.